Great progress has been made in the last 5 years in intravascular imaging of coronary arteries. It is the fundamental premise of this proposal, however, that current intravascular imaging devices can be dramatically improved and extended to provide more than diagnostic information alone. In particular, images of tissue hardness (i.e., elasticity) may provide critical feedback to both guide therapy and predict the likelihood of eventual restenosis. In effect, such elasticity images may allow the clinician to "feel" the arterial wall while performing catheter based procedures. To generate mechanical images of coronary arteries, an ultrasound imaging system must be integrated into a controlled mechanical deformation device resident in the lumen of the vessel. The ultrasound imager proposed for this device is a catheter based array system that can dynamically focus an ultrasound beam over a large depth of field using only a single connection between the catheter tip and the imaging console. Although simple in construction, it has the potential to produce high resolution images of coronary vessels. The array transducer is placed within a conventional balloon angioplasty catheter, where the balloon intersects the imaging plane. By slowing and continuously deforming the arterial wall with the balloon while simultaneously imaging with the catheter array, data can be acquired to image the elastic properties of the wall. Since elasticity correlates well with the human sense of touch, mechanical images may allow the clinician to "palpate" coronary vessels during diagnostic and therapeutic procedures. As part of the proposed research plan, all technical issues related to this system, including motion artifacts, specific image reconstruction algorithms, deformation measurements and custom probes, will be addressed. It is one of the primary objectives of this proposal to construct a prototype system demonstrating the capabilities of mechanical imaging of coronary arteries.